Final Report Summary - SAFTINSPECT (Ultrasonic Synthetic Aperture Focusing Technique for Inspection of Railway Crossings (Frogs))
Executive Summary:
The European rail infrastructure employs high manganese steel, components at safety critical locations such as crossings due to its very high material toughness and work-hardening properties. When crossings are in service, restricted access to these assets limits the range of NDT techniques available to those capable of inspection from the top surface. Conventional ultrasonic inspection of high manganese steel is ineffective due to the inherent coarse grain structure. Since radiography cannot be implemented in the field due to cost and stringent health and safety regulations, inspections are limited to periodic surface inspection techniques such as visual and dye penetrant inspection. The major concern with this is that defects such as cracks may exceed the critical defect tolerance without breaking the surface. This causes a risk to public safety and increases the life cycle costs, as by the time defects are detected they may be so large that they cannot be repaired, resulting in costly replacement.
The SAFTInspect consortium has successfully designed, developed and manufactured a complete automated ultrasonic inspection prototype system for inspection of sub-surface flaws in high manganese steel railway crossings. The system has been tested and validated in both a laboratory and trackside environment during the field trials held in Lulea, northern Sweden. Validation trials in both the laboratory and field environment were highly successful and demonstrated the ability of the system to detect and size sub-surface cracking at the critical nose region of the crossings. Trials also demonstrated the ability of the SAFTInspect system to perform in a real onsite environment without any significant degrading effects from adverse ambient conditions such as electrical interference from overhead power lines or freezing temperatures.
In brief summary, the potential benefits to railway operators and maintenance contractors resulting from the success of the SAFTInspect project include:
• Improved levels of safety for the railway industry and its customers, due to increased probability of detection of sub-surface flaws using the novel ultrasonic SAFT inspection system.
• Potential for reduced cost and improved reliability of pre-service examination of crossings, as sub-surface flaws may be reliably detected prior to rail being placed in-service.
• Extended asset life time and reduced Life Cycle Cost (LCC) as cracks which occur during service may be detected at an early stage in their growth cycle, allowing strategic monitoring and planning to be undertaken to manage the asset condition.
• Minimum down time due to the highly automated SAFTInspect inspection system.
Project Context and Objectives:
The European rail infrastructure employs high manganese steel components at safety critical locations such as crossings due to its very high material toughness and work-hardening properties. When crossings are in service, restricted access to these assets limits the range of NDT techniques available to those capable of inspection from the top surface. Conventional ultrasonic inspection of high manganese steel is ineffective due to the inherent coarse grain structure. The highly anisotropic and non-homogeneous material properties; low material penetration, high scattering and beam divergence contribute to low signal-to-noise ratio (SNR) of reflected signals. Since radiography cannot be implemented in the field due to cost and stringent health and safety regulations, inspections are limited to periodic surface inspection techniques. The major concern with this is that defects such as cracks may exceed the critical defect tolerance without breaking the surface. This causes a risk to public safety and increases the LCC, as by the time defects are detected they may be so large that they cannot be repaired, resulting in costly replacement.
The primary benefits resulting from the SAFTInspect project will be:
• Improved levels of safety due to increased probability of detection from spatial averaging and automated defect recognition and sentencing.
• Improved reliability of pre-service examination, as sub-surface flaws may be reliably detected prior to rail being placed in-service.
• Extended asset life time and reduced LCC as cracks which occur during service may be detected at an early stage in their growth cycle, allowing strategic monitoring and planning to be undertaken to manage the asset condition.
• Minimum down time due to highly automated inspection and minimal mechanical movement.
The SAFTInspect project aims to enable efficient in-service sub-surface inspection of manganese rail crossings by applying an ultrasonic inspection technique called Synthetic Aperture Focusing Technique (SAFT). SAFT utilises very large, synthesised probe apertures combined with advanced signal processing algorithms to offer an ultrasonic inspection technique with enhanced SNR. The SNR benefits of such techniques for use in coarse grained and anisotropic materials (such as high manganese rails) have been realised within academic institutes, but the technique has yet to be developed and commercialised for industrial NDT application. In conjunction with the SAFT technique, a 2D array probe was developed to enable beam steering to maximise material coverage while limiting mechanical movement during in-service inspections where surface access is limited. If track operators/maintainers can detect flaws at an early stage in their growth cycle, they can be monitored and routinely assessed, leading to increased levels of safety and reduced costs for rail operators.
The project has Scientific, Technology and Integration Objectives as detailed below:
Scientific Objectives:
• Demonstrate an improved SNR (predicted improvement >3dB) in comparison to conventional ultrasonic techniques.
Technology Development Objectives:
• Demonstrate SAFT algorithm capability to inspect the entire critical region of the high manganese steel crossing, therefore facilitating full volume inspection of the rail asset from its top surface.
• Quantitatively show an increased successful flaw detection rate of >50% using the SAFT algorithm in comparison in conventional ultrasonic techniques through ‘blind trial’ testing
Integration Objectives:
• To specify, design and assemble prototype inspection hardware and software capable of critical volume inspection within the entire critical region of in-situ rail crossings from top surface.
• Reduce inspection time of in-service inspection from 1 hour using existing techniques to 40 minutes per asset using the integrated SAFT inspection prototype system, yielding a reduced maintenance cost of €500/MGT per frog.
Project Results:
Integrated inspection system (Foreground IP):
The prototype SAFTInspect automated motorised and encoded scanner system has been designed and manufactured to facilitate fully automated movement of the transducer over the top surface of the rail crossing. The scanning system is comprised of several key components including:
• 4 axes (X, Y, Z, θ) scanner: 2 motorised and 2 encoded compliance axes
• Probe holder and irrigation system
• Ceramic/PVDF ultrasonic annular array transducer
• Ultrasonic pulser-receiver
• Desktop computer
• Scanner control software
• SAFT imaging reconstruction software
Automated motorised movement of the probe over the crossing critical area (150mm – 650mm back from the crossing nose point), is achieved using an (X, Y, Z, θ) motorised encoded scanner. A 2D annular ultrasonic probe is used to interrogate the crossing and utilises a ceramic transmit material and polymer receiver material, which maximises the probes acoustic efficiency on transmit and receive. The probe attaches to the main scanner via a probe holder, which holds the probe in position and utilises ball-bearing casters on its underside to achieve smooth movement over the top surface of the crossing.
An Olympus Omniscan MX pulser-receiver system is used to trigger the ultrasonic transducer and acquire the raw data. This system was chosen as it is highly ruggedized for site inspection and commonly used in industry. Both the scanner control software and SAFT reconstruction software are operated from a desktop PC.
The control software controls the scanner movement and facilitates automated motorised scanning over the top surface of railway crossings. This is largely achieved using automatic edge detection algorithms, which detects the edge of the crossing using an inclinometer to monitor the tilt angle of the probe. Once a particular tilt angle is exceeded the control software triggers a change in scanning direction which ensures the transducer remains coupled to the top surface of the crossing. The edge detection functionality negates the need for manually measuring the top surface profile of the crossing, as well as the need to manually enter the scan coordinates, which would be highly time consuming and prone to operator error. Finally, the SAFT reconstruction software enables raw data to be reconstructed into focussed 2D and 3D images for analysis by an NDT operator.
In addition to the foreground IP associated with the complete integrated scanning system, many of the system components, developed within the project, also have significant Foreground IP associated with them in their own right. As such, these system components are discussed in turn in the proceeding paragraphs.
Bespoke 2D annular transducer (Foreground IP): Within the project a highly novel ultrasonic transducer has been developed, which offers excellent signal to noise ratio and sensitivity to subsurface flaws in high manganese steel. The transducer has a 2D annular element configuration which was used in the final transducer design due to its axial symmetry. This axial symmetry allowed a uniform energy distribution to be created 360 degrees about the transducer’s axial axis. This uniform energy distribution in turn allowed for synthetic beam steering 360 degrees about the transducer and thus enabled the critical volume coverage (5-50mm) of the critical nose region.
To maximise the sensitivity of the transducer, a highly novel dual layered transducer was designed and manufactured. To summarise, two commonly used piezoelectric materials are PZT piezoceramic and PVDF Piezopolymer. Both of these materials have different piezoelectric properties which make them best suited for different applications. In short, PZT is good at converting electrical energy into mechanical energy and is therefore good at transmitting ultrasound whilst for PVDF the reverse is true and it can be considered as a good receiver of ultrasound. A key design feature of this probe is the relative placement of the transmit and receive elements. The low acoustic impedance of PVDF and the fact that it is a thin (<30µm or <<0.1λ) film thickness mean that the receive elements can be placed directly in front of the transmitting elements without causing significant distortion or attenuation of the transmitted signal. This arrangement removes the need to share surface area between transmit and receive elements and allows the best possible use of available space.
With this in mind, the first tier of the transducer ‘Tier 1’ was manufactured from piezo-ceramic material (optimal for transmitting ultrasound) and was used to transmit ultrasonic energy into the manganese steel crossing. Tier ‘2’ had an identical footprint and was laminated over the tier ‘1’ array using piezo-polymer material (optimum for receiving ultrasound). This highly novel combination of ceramic transmitter and polymer receiver allowed the maximum amount of energy to be transmitted into the material while still being highly sensitive to signals on receive.
This knowledge of manufacturing processes and the validation work performed within the project will enable sales of a new product line in its own right. Additional sales of this transducer will form part of the supply chain of the SAFTInspect system.
SAFT software (Foreground IP): Presently industrial ultrasonic inspection of railway infrastructure is performed using conventional or phased array ultrasonic inspection techniques. However these techniques are not used for inspection of manganese steel crossings due to the poor SNR and sensitivity levels caused by high levels of coherent back-scatter emanating from the coarse material grain structure. The SAFT reconstruction algorithms, which are central to the SAFT software, have been shown within the SAFTInspect project to offer improved SNR, sensitivity and depth of penetration in high manganese steel crossings.
The algorithms enable greater inspection performance for when inspecting coarse grained materials due to their inherent ability to spatially average out coherent noise such as back-scatter from material grain boundaries. The overall SAFT software was therefore of primary importance in achieving the high performance levels achieved with the SAFTInspect system.
The SAFT software is a powerful but user friendly package which takes raw encoded ultrasound data and reconstructs it into high resolution 2D or 3D images. In order to maximise the usability of the software, a graphical user interface (GUI) was developed, which enabled quick and easy use of the software by NDT operators, without the requirement for a specialist background in computer programming.
The main user interface screen allows the operator to simply input raw encoded data from file and then reconstruct this raw data into a 2D or 3D image. Once reconstruction is complete a ‘top down’ preview of the reconstruction appears in the screen. In the ‘Visualisation Window’, the operator can view, manipulate and analyse the data in 2D slices or rendered 3D image formats. The image manipulation functionality within the visualisation window includes:
• Zoom
• Rotation
• Data smoothing
• Toggle 2D slice and 3D image reconstruction. Slices may be added by the operator in the x, y and z planes as required.
• Camera lighting
• Probe scan path visualisation
The SAFT software also allows for acquired inspection data to be compared with historical data in order to assess crack propagation over time. Algorithms were developed which allow crack growth to be monitored and flagged to alert the operator by indicating crack growth as a unique colour in the software visualisation window. The ability to monitor crack propagation over time enables more accurate and informed fitness-for-service assessments leading to reduced product life cycles costs and improved safety for the industry and its customers.
Automated encoded scanner (Foreground IP): The automated motorised encoded scanner forms the primary sub-assembly of the integrated SAFTInspect system. The scanner comprises of several major components including a main frame, which is a Cartesian X, Y, Z, θ scanner manufactured from extruded aluminium. The X and Y axis are both encoded and motorised in order to allow translation of the ultrasonic transducer over the top surface of high manganese steel crossings. The Z and θ encoded axes were designed and manufactured to be compliant in order to allow the sensor to conform to the irregular surface profile of crossings during inspection. The rotational axis was encoded using an inclinometer that measures the tilt of the probe holder over the irregular surface profile of the crossing. Similarly to the X, Y axes, all signals from the encoders were communicated to the host PC via the enclosure unit mounted on the side of the scanner.
The probe holder integrated with the main scanner of the SAFTInspect inspection system has been designed and manufactured to perform several functions. Firstly, it houses the annular array transducer and holds it in position at a fixed stand-off for inspection. Secondly, it forms an integral part of the irrigation system as it houses two squirters on its underside, as well as forming the water chamber. The water chamber enables efficient transfer of ultrasound from the transducer elements and steel crossing. Finally, the probe holder ensures smooth movement of the transducer over the crossing through the use of a ball bearing system and conformable membrane pad, situated on its underside. These ball bearing casters can be adjusted to alter the standoff of the holder from the crossing as required.
Control Software (Foreground IP): The SAFTInspect control system provides fully automated or manual control of the scanner over the top surface of crossings. The software package allows the operator to perform automated scans as well as manually scanning of the transducer in the X and Y axes. Automated scanning is achieved largely through the ability of the control software to detect the edges of the crossing via its intelligent ‘edge detection’ functionality, which ensures the transducer always remains coupled to the top surface of the crossing and allows inspection of the whole critical area with minimum operator interference.
System performance validation (Results): Within the SAFTInspect project numerous tests have been performed to assess the performance and validate the SAFTInspect system against the performance criteria outlined in the specification developed at the start of the project. The criteria in the specification required the system to reach a particular level of performance in the following categories:
• Axial resolution
• Sensitivity
• Signal to noise ratio
• Lateral resolution
• Penetration depth
Through empirical studies the SAFTInspect system has been shown to either meet or exceed the system requirements outlined in the defined specifications.
In addition to the manganese steel components containing machined artificial flaws, validation work was performed on a full scale crossing, removed from service due to a surface breaking longitudinal crack in the nose region of the crossing. The SAFTInspect system was shown to detect the longitudinal crack with good SNR above the noise level. The result from the SAFTInspect system was partially validated by performing dye penetrant inspection (surface inspection technique) to identify the size of the cracking that could be seen on the surface. As expected the SAFTInspect system predicted that the crack extended further into the material than what could be seen on the surface. To categorically determine the sub-surface extent of the longitudinal crack, sectioning and microscopy would be required. However this was not possible due to the high value of the component.
Validation in adverse conditions: In order to increase the technology readiness and maturity of the SAFTInspect system, tests were also performed in an onsite environment and using components containing real crack defects. Field trials were conducted in freezing winter conditions in northern Sweden 28-29 October 2014 in order to assess performance under the most extreme adverse conditions which were likely to be encountered. The system was shown to perform well under adverse conditions and was unaffected by the ambient freezing weather conditions. Electrical interference from overhead power lines (used to power majority of rolling stock in Sweden) was also shown to have negligible effect on the system performance.
During lab trials a section of crossing which had been removed from service due to pitting was sourced. Unfortunately it was to be proven that the level of pitting present on this particular crossing was too excessive to inspect with any form of ultrasonic inspection equipment, including the SAFTInspect system. However, it was concluded that this was an extreme case where the crossing was removed from service due to the high level of pitting.
Potential Impact:
The SAFTInspect project will create significant social and economic impact for the SME partners as well as for the railway industry and its customers through the development of a highly innovative ultrasonic non-destructive testing inspection system, which for the first time will enable sub-surface inspection of crossings to be performed while crossings are in-service. Since inspection performed during manufacture uses radiographic techniques, the SAFTInspect system also offers the potential to significantly reduce the cost and health risks for inspections performed at this stage.
Impact on in-service market
Railway operators and maintenance providers have high motivation to procure the SAFTInspect system as presently in-service inspection is limited to surface techniques including visual and dye penetrant. The lack of information on the materials sub-surface condition results in operators being required to make conservative structural integrity assessments leading to increased life cycle costs. In addition to this, by the time flaws are detected using surface limited inspection techniques, the structural integrity of the safety critical components can already be compromised. This leads to an immediate action of repair or replace, which further increases the cost and time due to unscheduled maintenance. The ability to detect and characterise sub-surface flaws means that defects can be detected at an earlier stage in their growth cycle and before they significantly compromise the integrity of the asset. As such the SAFTInspect system will enable strategic monitoring and scheduled maintenance of crossings leading to reduced life cycle costs and increased levels of safety for the rail industry and its customers.
Impact during manufacture process
Crossing manufacturers currently use radiographic inspection to determine the integrity of crossings prior to use in-service, which is expensive and has stringent health and safety regulations due to the risks associated with ionising radiation. Also, due to the high associated costs manufacturers only inspect batches of crossings using the ALARA (as low as reasonable achievable) method, which means potentially only 1 in 30 crossings will actually be inspected, resulting in an increased likelihood of a defective crossing being issued for service.
Manufacturers therefore have high motivation to use an ultrasonic technique, which by comparison will be relatively inexpensive, requires lower skilled operators and has no serious health risks. As such the SAFTInspect system can lead to significant economic savings for crossing manufacturers, as well as reducing the health risk of operators coming in contact with ionising radiation associated with radiography.
In addition to the health risks of the inspection operator, the ability of the SAFTInspect system to potentially inspection all crossings on a production line means that the probability of a defective crossing been issued for service is greatly reduced, leading to increased safety for the railway industry and its customers.
Additional impact
In addition to sales and licencing of components which form the integrated SAFTInspect system, SME partners who own the IPR of the individual SAFTInspect system components will also reap economic benefit from sales and licencing in other markets and product lines:
Within the project, a novel x, y, z, ɵ scanner owned by MCT may also be applied to numerous applications which require automated translation of a sensor over a relatively flat surface and as such may form part of the supply chain for a wide range of applications within industries such as rail, aerospace, oil and gas and nuclear.
The SAFT algorithms, which are central to the SAFT reconstruction software, offer improved SNR, sensitivity and depth of penetration in coarse grained materials such as high manganese steel through the ability to spatially average out grain noise. The Graphical User Interface which has been included in the SAFT software makes these algorithms accessible to people without programming and software knowledge. As such, this software can be used by SME partner M8 for inspection of crossings. In addition, the SAFT software may also be used for inspection of other coarse grained materials such as copper used for nuclear storage or stainless steel pipework and vessels in the nuclear and oil and gas industries.
Finally, a highly novel ultrasonic transducer has been developed which achieves very high levels of sensitivity and SNR by using a 2 tier array configuration. Tier ‘1’ of the array is the transmit tier, manufactured from piezo-ceramic material (optimal for transmitting ultrasound). Tier ‘2’ has an identical footprint and has been laminated over the tier ‘1’ array using piezo-polymer (PVDF) material (optimum for receiving ultrasound). This novel combination allows maximum energy to be transmitted into the material while still being highly sensitive to signals on receive. This knowledge of manufacturing processes and the validation work performed within the project will enable sales of a new product line in its own right for SME partner PA.
Main Dissemination of results
A large number of dissemination activities were undertaken in order to raise the profile of the SAFTInspect project and promote the SAFTInspect system in the Railway industry, NDT industry and academia. Conference presentations, exhibitions and conference/journal publications were identified as an effective means of promoting the SAFTInspect project to academics and railway and non-destructive testing (NDT) experts with an interest in innovation and novel concepts/prototypes for future deployment.
The original electronic copies of all physical dissemination material, which includes brochures, posters and conference/journal papers, have been uploaded into the private members area of the SAFTInspect website. Moving forwards beyond the completion of the SAFTInspect project, this allows the SME members and other stakeholders to access and reproduce material, free issue, as and when required. In addition the HD video (.MP4 file format), which was too large to upload to the project website, has been uploaded to a ‘Share File’ site for download by the consortium. Again this enables each consortium member to reproduce the video footage in a number of formats as and when required (DVD, YouTube etc.).
In addition to the dissemination activities given at the conferences and exhibitions, End User TRV gave a presentation to a specific and targeted audience of senior railway operator and maintenance managers. This presentation gave an overview of the SAFTInspect project and outlined the benefits of the system over existing industrial technologies. The presentation was given by TRV on behalf of the SME partners in the consortium, as it was felt that large railway operators and maintenance managers would be more likely to attend and listen to another large enterprise in the industry as appose to an SME organisation.
In summary the following dissemination activities have been performed during the SAFTInspect project:
• 2 poster presentations at conference
• 2 paper presentations at conference
• Attended 2 exhibitions to promote SAFTInspect project
• 3 journal/conference paper publications
• Brochures published in 3 different languages, which have been distributed at numerous events
• Up-to-date project website
• HD video of field trials published on YouTube, project website and DVD.
• Generated a large floor-standing SAFTInspect poster
• Generated a large conference poster for IEEE ultrasonic symposium.
• TRV presented and promoted SAFTInspect to a number of managers working in large EU railway organisations
List of Websites:
A project website was set up at the start of the project for dissemination of results, as well as to facilitate and act as a communication tool for the consortium. The website consists of two main areas: one accessible to the public, and one only accessible by the members of the consortium. The project website address is: www.saftinspect.eu
Primary contact:
Antonio Puyol (AIRTREN)
antonio.puyol@airtren.com
+34 609 04 68 75
The European rail infrastructure employs high manganese steel, components at safety critical locations such as crossings due to its very high material toughness and work-hardening properties. When crossings are in service, restricted access to these assets limits the range of NDT techniques available to those capable of inspection from the top surface. Conventional ultrasonic inspection of high manganese steel is ineffective due to the inherent coarse grain structure. Since radiography cannot be implemented in the field due to cost and stringent health and safety regulations, inspections are limited to periodic surface inspection techniques such as visual and dye penetrant inspection. The major concern with this is that defects such as cracks may exceed the critical defect tolerance without breaking the surface. This causes a risk to public safety and increases the life cycle costs, as by the time defects are detected they may be so large that they cannot be repaired, resulting in costly replacement.
The SAFTInspect consortium has successfully designed, developed and manufactured a complete automated ultrasonic inspection prototype system for inspection of sub-surface flaws in high manganese steel railway crossings. The system has been tested and validated in both a laboratory and trackside environment during the field trials held in Lulea, northern Sweden. Validation trials in both the laboratory and field environment were highly successful and demonstrated the ability of the system to detect and size sub-surface cracking at the critical nose region of the crossings. Trials also demonstrated the ability of the SAFTInspect system to perform in a real onsite environment without any significant degrading effects from adverse ambient conditions such as electrical interference from overhead power lines or freezing temperatures.
In brief summary, the potential benefits to railway operators and maintenance contractors resulting from the success of the SAFTInspect project include:
• Improved levels of safety for the railway industry and its customers, due to increased probability of detection of sub-surface flaws using the novel ultrasonic SAFT inspection system.
• Potential for reduced cost and improved reliability of pre-service examination of crossings, as sub-surface flaws may be reliably detected prior to rail being placed in-service.
• Extended asset life time and reduced Life Cycle Cost (LCC) as cracks which occur during service may be detected at an early stage in their growth cycle, allowing strategic monitoring and planning to be undertaken to manage the asset condition.
• Minimum down time due to the highly automated SAFTInspect inspection system.
Project Context and Objectives:
The European rail infrastructure employs high manganese steel components at safety critical locations such as crossings due to its very high material toughness and work-hardening properties. When crossings are in service, restricted access to these assets limits the range of NDT techniques available to those capable of inspection from the top surface. Conventional ultrasonic inspection of high manganese steel is ineffective due to the inherent coarse grain structure. The highly anisotropic and non-homogeneous material properties; low material penetration, high scattering and beam divergence contribute to low signal-to-noise ratio (SNR) of reflected signals. Since radiography cannot be implemented in the field due to cost and stringent health and safety regulations, inspections are limited to periodic surface inspection techniques. The major concern with this is that defects such as cracks may exceed the critical defect tolerance without breaking the surface. This causes a risk to public safety and increases the LCC, as by the time defects are detected they may be so large that they cannot be repaired, resulting in costly replacement.
The primary benefits resulting from the SAFTInspect project will be:
• Improved levels of safety due to increased probability of detection from spatial averaging and automated defect recognition and sentencing.
• Improved reliability of pre-service examination, as sub-surface flaws may be reliably detected prior to rail being placed in-service.
• Extended asset life time and reduced LCC as cracks which occur during service may be detected at an early stage in their growth cycle, allowing strategic monitoring and planning to be undertaken to manage the asset condition.
• Minimum down time due to highly automated inspection and minimal mechanical movement.
The SAFTInspect project aims to enable efficient in-service sub-surface inspection of manganese rail crossings by applying an ultrasonic inspection technique called Synthetic Aperture Focusing Technique (SAFT). SAFT utilises very large, synthesised probe apertures combined with advanced signal processing algorithms to offer an ultrasonic inspection technique with enhanced SNR. The SNR benefits of such techniques for use in coarse grained and anisotropic materials (such as high manganese rails) have been realised within academic institutes, but the technique has yet to be developed and commercialised for industrial NDT application. In conjunction with the SAFT technique, a 2D array probe was developed to enable beam steering to maximise material coverage while limiting mechanical movement during in-service inspections where surface access is limited. If track operators/maintainers can detect flaws at an early stage in their growth cycle, they can be monitored and routinely assessed, leading to increased levels of safety and reduced costs for rail operators.
The project has Scientific, Technology and Integration Objectives as detailed below:
Scientific Objectives:
• Demonstrate an improved SNR (predicted improvement >3dB) in comparison to conventional ultrasonic techniques.
Technology Development Objectives:
• Demonstrate SAFT algorithm capability to inspect the entire critical region of the high manganese steel crossing, therefore facilitating full volume inspection of the rail asset from its top surface.
• Quantitatively show an increased successful flaw detection rate of >50% using the SAFT algorithm in comparison in conventional ultrasonic techniques through ‘blind trial’ testing
Integration Objectives:
• To specify, design and assemble prototype inspection hardware and software capable of critical volume inspection within the entire critical region of in-situ rail crossings from top surface.
• Reduce inspection time of in-service inspection from 1 hour using existing techniques to 40 minutes per asset using the integrated SAFT inspection prototype system, yielding a reduced maintenance cost of €500/MGT per frog.
Project Results:
Integrated inspection system (Foreground IP):
The prototype SAFTInspect automated motorised and encoded scanner system has been designed and manufactured to facilitate fully automated movement of the transducer over the top surface of the rail crossing. The scanning system is comprised of several key components including:
• 4 axes (X, Y, Z, θ) scanner: 2 motorised and 2 encoded compliance axes
• Probe holder and irrigation system
• Ceramic/PVDF ultrasonic annular array transducer
• Ultrasonic pulser-receiver
• Desktop computer
• Scanner control software
• SAFT imaging reconstruction software
Automated motorised movement of the probe over the crossing critical area (150mm – 650mm back from the crossing nose point), is achieved using an (X, Y, Z, θ) motorised encoded scanner. A 2D annular ultrasonic probe is used to interrogate the crossing and utilises a ceramic transmit material and polymer receiver material, which maximises the probes acoustic efficiency on transmit and receive. The probe attaches to the main scanner via a probe holder, which holds the probe in position and utilises ball-bearing casters on its underside to achieve smooth movement over the top surface of the crossing.
An Olympus Omniscan MX pulser-receiver system is used to trigger the ultrasonic transducer and acquire the raw data. This system was chosen as it is highly ruggedized for site inspection and commonly used in industry. Both the scanner control software and SAFT reconstruction software are operated from a desktop PC.
The control software controls the scanner movement and facilitates automated motorised scanning over the top surface of railway crossings. This is largely achieved using automatic edge detection algorithms, which detects the edge of the crossing using an inclinometer to monitor the tilt angle of the probe. Once a particular tilt angle is exceeded the control software triggers a change in scanning direction which ensures the transducer remains coupled to the top surface of the crossing. The edge detection functionality negates the need for manually measuring the top surface profile of the crossing, as well as the need to manually enter the scan coordinates, which would be highly time consuming and prone to operator error. Finally, the SAFT reconstruction software enables raw data to be reconstructed into focussed 2D and 3D images for analysis by an NDT operator.
In addition to the foreground IP associated with the complete integrated scanning system, many of the system components, developed within the project, also have significant Foreground IP associated with them in their own right. As such, these system components are discussed in turn in the proceeding paragraphs.
Bespoke 2D annular transducer (Foreground IP): Within the project a highly novel ultrasonic transducer has been developed, which offers excellent signal to noise ratio and sensitivity to subsurface flaws in high manganese steel. The transducer has a 2D annular element configuration which was used in the final transducer design due to its axial symmetry. This axial symmetry allowed a uniform energy distribution to be created 360 degrees about the transducer’s axial axis. This uniform energy distribution in turn allowed for synthetic beam steering 360 degrees about the transducer and thus enabled the critical volume coverage (5-50mm) of the critical nose region.
To maximise the sensitivity of the transducer, a highly novel dual layered transducer was designed and manufactured. To summarise, two commonly used piezoelectric materials are PZT piezoceramic and PVDF Piezopolymer. Both of these materials have different piezoelectric properties which make them best suited for different applications. In short, PZT is good at converting electrical energy into mechanical energy and is therefore good at transmitting ultrasound whilst for PVDF the reverse is true and it can be considered as a good receiver of ultrasound. A key design feature of this probe is the relative placement of the transmit and receive elements. The low acoustic impedance of PVDF and the fact that it is a thin (<30µm or <<0.1λ) film thickness mean that the receive elements can be placed directly in front of the transmitting elements without causing significant distortion or attenuation of the transmitted signal. This arrangement removes the need to share surface area between transmit and receive elements and allows the best possible use of available space.
With this in mind, the first tier of the transducer ‘Tier 1’ was manufactured from piezo-ceramic material (optimal for transmitting ultrasound) and was used to transmit ultrasonic energy into the manganese steel crossing. Tier ‘2’ had an identical footprint and was laminated over the tier ‘1’ array using piezo-polymer material (optimum for receiving ultrasound). This highly novel combination of ceramic transmitter and polymer receiver allowed the maximum amount of energy to be transmitted into the material while still being highly sensitive to signals on receive.
This knowledge of manufacturing processes and the validation work performed within the project will enable sales of a new product line in its own right. Additional sales of this transducer will form part of the supply chain of the SAFTInspect system.
SAFT software (Foreground IP): Presently industrial ultrasonic inspection of railway infrastructure is performed using conventional or phased array ultrasonic inspection techniques. However these techniques are not used for inspection of manganese steel crossings due to the poor SNR and sensitivity levels caused by high levels of coherent back-scatter emanating from the coarse material grain structure. The SAFT reconstruction algorithms, which are central to the SAFT software, have been shown within the SAFTInspect project to offer improved SNR, sensitivity and depth of penetration in high manganese steel crossings.
The algorithms enable greater inspection performance for when inspecting coarse grained materials due to their inherent ability to spatially average out coherent noise such as back-scatter from material grain boundaries. The overall SAFT software was therefore of primary importance in achieving the high performance levels achieved with the SAFTInspect system.
The SAFT software is a powerful but user friendly package which takes raw encoded ultrasound data and reconstructs it into high resolution 2D or 3D images. In order to maximise the usability of the software, a graphical user interface (GUI) was developed, which enabled quick and easy use of the software by NDT operators, without the requirement for a specialist background in computer programming.
The main user interface screen allows the operator to simply input raw encoded data from file and then reconstruct this raw data into a 2D or 3D image. Once reconstruction is complete a ‘top down’ preview of the reconstruction appears in the screen. In the ‘Visualisation Window’, the operator can view, manipulate and analyse the data in 2D slices or rendered 3D image formats. The image manipulation functionality within the visualisation window includes:
• Zoom
• Rotation
• Data smoothing
• Toggle 2D slice and 3D image reconstruction. Slices may be added by the operator in the x, y and z planes as required.
• Camera lighting
• Probe scan path visualisation
The SAFT software also allows for acquired inspection data to be compared with historical data in order to assess crack propagation over time. Algorithms were developed which allow crack growth to be monitored and flagged to alert the operator by indicating crack growth as a unique colour in the software visualisation window. The ability to monitor crack propagation over time enables more accurate and informed fitness-for-service assessments leading to reduced product life cycles costs and improved safety for the industry and its customers.
Automated encoded scanner (Foreground IP): The automated motorised encoded scanner forms the primary sub-assembly of the integrated SAFTInspect system. The scanner comprises of several major components including a main frame, which is a Cartesian X, Y, Z, θ scanner manufactured from extruded aluminium. The X and Y axis are both encoded and motorised in order to allow translation of the ultrasonic transducer over the top surface of high manganese steel crossings. The Z and θ encoded axes were designed and manufactured to be compliant in order to allow the sensor to conform to the irregular surface profile of crossings during inspection. The rotational axis was encoded using an inclinometer that measures the tilt of the probe holder over the irregular surface profile of the crossing. Similarly to the X, Y axes, all signals from the encoders were communicated to the host PC via the enclosure unit mounted on the side of the scanner.
The probe holder integrated with the main scanner of the SAFTInspect inspection system has been designed and manufactured to perform several functions. Firstly, it houses the annular array transducer and holds it in position at a fixed stand-off for inspection. Secondly, it forms an integral part of the irrigation system as it houses two squirters on its underside, as well as forming the water chamber. The water chamber enables efficient transfer of ultrasound from the transducer elements and steel crossing. Finally, the probe holder ensures smooth movement of the transducer over the crossing through the use of a ball bearing system and conformable membrane pad, situated on its underside. These ball bearing casters can be adjusted to alter the standoff of the holder from the crossing as required.
Control Software (Foreground IP): The SAFTInspect control system provides fully automated or manual control of the scanner over the top surface of crossings. The software package allows the operator to perform automated scans as well as manually scanning of the transducer in the X and Y axes. Automated scanning is achieved largely through the ability of the control software to detect the edges of the crossing via its intelligent ‘edge detection’ functionality, which ensures the transducer always remains coupled to the top surface of the crossing and allows inspection of the whole critical area with minimum operator interference.
System performance validation (Results): Within the SAFTInspect project numerous tests have been performed to assess the performance and validate the SAFTInspect system against the performance criteria outlined in the specification developed at the start of the project. The criteria in the specification required the system to reach a particular level of performance in the following categories:
• Axial resolution
• Sensitivity
• Signal to noise ratio
• Lateral resolution
• Penetration depth
Through empirical studies the SAFTInspect system has been shown to either meet or exceed the system requirements outlined in the defined specifications.
In addition to the manganese steel components containing machined artificial flaws, validation work was performed on a full scale crossing, removed from service due to a surface breaking longitudinal crack in the nose region of the crossing. The SAFTInspect system was shown to detect the longitudinal crack with good SNR above the noise level. The result from the SAFTInspect system was partially validated by performing dye penetrant inspection (surface inspection technique) to identify the size of the cracking that could be seen on the surface. As expected the SAFTInspect system predicted that the crack extended further into the material than what could be seen on the surface. To categorically determine the sub-surface extent of the longitudinal crack, sectioning and microscopy would be required. However this was not possible due to the high value of the component.
Validation in adverse conditions: In order to increase the technology readiness and maturity of the SAFTInspect system, tests were also performed in an onsite environment and using components containing real crack defects. Field trials were conducted in freezing winter conditions in northern Sweden 28-29 October 2014 in order to assess performance under the most extreme adverse conditions which were likely to be encountered. The system was shown to perform well under adverse conditions and was unaffected by the ambient freezing weather conditions. Electrical interference from overhead power lines (used to power majority of rolling stock in Sweden) was also shown to have negligible effect on the system performance.
During lab trials a section of crossing which had been removed from service due to pitting was sourced. Unfortunately it was to be proven that the level of pitting present on this particular crossing was too excessive to inspect with any form of ultrasonic inspection equipment, including the SAFTInspect system. However, it was concluded that this was an extreme case where the crossing was removed from service due to the high level of pitting.
Potential Impact:
The SAFTInspect project will create significant social and economic impact for the SME partners as well as for the railway industry and its customers through the development of a highly innovative ultrasonic non-destructive testing inspection system, which for the first time will enable sub-surface inspection of crossings to be performed while crossings are in-service. Since inspection performed during manufacture uses radiographic techniques, the SAFTInspect system also offers the potential to significantly reduce the cost and health risks for inspections performed at this stage.
Impact on in-service market
Railway operators and maintenance providers have high motivation to procure the SAFTInspect system as presently in-service inspection is limited to surface techniques including visual and dye penetrant. The lack of information on the materials sub-surface condition results in operators being required to make conservative structural integrity assessments leading to increased life cycle costs. In addition to this, by the time flaws are detected using surface limited inspection techniques, the structural integrity of the safety critical components can already be compromised. This leads to an immediate action of repair or replace, which further increases the cost and time due to unscheduled maintenance. The ability to detect and characterise sub-surface flaws means that defects can be detected at an earlier stage in their growth cycle and before they significantly compromise the integrity of the asset. As such the SAFTInspect system will enable strategic monitoring and scheduled maintenance of crossings leading to reduced life cycle costs and increased levels of safety for the rail industry and its customers.
Impact during manufacture process
Crossing manufacturers currently use radiographic inspection to determine the integrity of crossings prior to use in-service, which is expensive and has stringent health and safety regulations due to the risks associated with ionising radiation. Also, due to the high associated costs manufacturers only inspect batches of crossings using the ALARA (as low as reasonable achievable) method, which means potentially only 1 in 30 crossings will actually be inspected, resulting in an increased likelihood of a defective crossing being issued for service.
Manufacturers therefore have high motivation to use an ultrasonic technique, which by comparison will be relatively inexpensive, requires lower skilled operators and has no serious health risks. As such the SAFTInspect system can lead to significant economic savings for crossing manufacturers, as well as reducing the health risk of operators coming in contact with ionising radiation associated with radiography.
In addition to the health risks of the inspection operator, the ability of the SAFTInspect system to potentially inspection all crossings on a production line means that the probability of a defective crossing been issued for service is greatly reduced, leading to increased safety for the railway industry and its customers.
Additional impact
In addition to sales and licencing of components which form the integrated SAFTInspect system, SME partners who own the IPR of the individual SAFTInspect system components will also reap economic benefit from sales and licencing in other markets and product lines:
Within the project, a novel x, y, z, ɵ scanner owned by MCT may also be applied to numerous applications which require automated translation of a sensor over a relatively flat surface and as such may form part of the supply chain for a wide range of applications within industries such as rail, aerospace, oil and gas and nuclear.
The SAFT algorithms, which are central to the SAFT reconstruction software, offer improved SNR, sensitivity and depth of penetration in coarse grained materials such as high manganese steel through the ability to spatially average out grain noise. The Graphical User Interface which has been included in the SAFT software makes these algorithms accessible to people without programming and software knowledge. As such, this software can be used by SME partner M8 for inspection of crossings. In addition, the SAFT software may also be used for inspection of other coarse grained materials such as copper used for nuclear storage or stainless steel pipework and vessels in the nuclear and oil and gas industries.
Finally, a highly novel ultrasonic transducer has been developed which achieves very high levels of sensitivity and SNR by using a 2 tier array configuration. Tier ‘1’ of the array is the transmit tier, manufactured from piezo-ceramic material (optimal for transmitting ultrasound). Tier ‘2’ has an identical footprint and has been laminated over the tier ‘1’ array using piezo-polymer (PVDF) material (optimum for receiving ultrasound). This novel combination allows maximum energy to be transmitted into the material while still being highly sensitive to signals on receive. This knowledge of manufacturing processes and the validation work performed within the project will enable sales of a new product line in its own right for SME partner PA.
Main Dissemination of results
A large number of dissemination activities were undertaken in order to raise the profile of the SAFTInspect project and promote the SAFTInspect system in the Railway industry, NDT industry and academia. Conference presentations, exhibitions and conference/journal publications were identified as an effective means of promoting the SAFTInspect project to academics and railway and non-destructive testing (NDT) experts with an interest in innovation and novel concepts/prototypes for future deployment.
The original electronic copies of all physical dissemination material, which includes brochures, posters and conference/journal papers, have been uploaded into the private members area of the SAFTInspect website. Moving forwards beyond the completion of the SAFTInspect project, this allows the SME members and other stakeholders to access and reproduce material, free issue, as and when required. In addition the HD video (.MP4 file format), which was too large to upload to the project website, has been uploaded to a ‘Share File’ site for download by the consortium. Again this enables each consortium member to reproduce the video footage in a number of formats as and when required (DVD, YouTube etc.).
In addition to the dissemination activities given at the conferences and exhibitions, End User TRV gave a presentation to a specific and targeted audience of senior railway operator and maintenance managers. This presentation gave an overview of the SAFTInspect project and outlined the benefits of the system over existing industrial technologies. The presentation was given by TRV on behalf of the SME partners in the consortium, as it was felt that large railway operators and maintenance managers would be more likely to attend and listen to another large enterprise in the industry as appose to an SME organisation.
In summary the following dissemination activities have been performed during the SAFTInspect project:
• 2 poster presentations at conference
• 2 paper presentations at conference
• Attended 2 exhibitions to promote SAFTInspect project
• 3 journal/conference paper publications
• Brochures published in 3 different languages, which have been distributed at numerous events
• Up-to-date project website
• HD video of field trials published on YouTube, project website and DVD.
• Generated a large floor-standing SAFTInspect poster
• Generated a large conference poster for IEEE ultrasonic symposium.
• TRV presented and promoted SAFTInspect to a number of managers working in large EU railway organisations
List of Websites:
A project website was set up at the start of the project for dissemination of results, as well as to facilitate and act as a communication tool for the consortium. The website consists of two main areas: one accessible to the public, and one only accessible by the members of the consortium. The project website address is: www.saftinspect.eu
Primary contact:
Antonio Puyol (AIRTREN)
antonio.puyol@airtren.com
+34 609 04 68 75